As seen in FIG. 1, the cryosurgical instrument most commonly used comprises a reservoir including a double metal wall vacuum bottle 10, modified for use with liquefied cryogen by provision of a collar 11 at the top thereof (shown only in FIG. 3) which encompasses the joint between the two metal walls, and by provision of a vent hole (not shown) in the bottom pan that protects the vacuum seal thereof. The collar 11 is provided with machined threads 12 (FIG. 3) to permit joining the vacuum bottle 10 to a cap 13 having threads 14 (FIG. 3) which mounts the control and delivery portion 15 of the instrument. The forerunner of the instrument of FIGS. 1 and 2 is set forth in U.S. Pat. No. 4,116,199. In recent years, the neck (upper outside portion) of the instrument has been fitted with a polyfoam collar 16 for an insulated grip, because the metal of the instrument becomes cold during use. However, the users hand may tend to slide and be forced to rest on the lip of the metal cap 13, which becomes very cold to the touch during use. To overcome this problem, a second foam collar 17 (FIG. 2) may be slipped over the upper part of the collar 16 and the cap 13; and a single large collar has been used instead of the two collars 16, 17.
However, the polyfoam collars that extend over the cap must be folded down (like a turtle neck sweater) or removed whenever the cap is removed for filling the instrument with cryogen. Furthermore, the collars cannot be sterilized in an autoclave, since the polyfoam will shrink into useless circlets. Therefore, devices using such collars cannot be used in a sterile theater, such as an operating room.